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* Bound public rate-limit buckets against attacker-keyed growth. Keep the NIP-13 PoW sender bypass, skip content-bucket minting on sender reject, and evict idle/oldest entries at a hard cap. Co-authored-by: Cursor <cursoragent@cursor.com> * Stop Cashu-looking text from skipping long-message guards. Oversized public content always collapses and takes the plain formatting path so remote tokens cannot force layout/regex DoS. Co-authored-by: Cursor <cursoragent@cursor.com> * Cap teleported geohash participant markers. Bound the set with FIFO eviction, clear it on channel switch, and prune markers that leave the visible participant list. Co-authored-by: Cursor <cursoragent@cursor.com> * Bound untrusted Nostr relay frames and event tags. Reject oversized inbound messages before JSON parse, cap tag arrays/values at decode, and stop logging raw tag contents. Co-authored-by: Cursor <cursoragent@cursor.com> * Fail soft when Noise handshake state is unexpectedly missing. Replace the initiator startHandshake force unwrap with a guard that throws invalidState instead of crashing. Co-authored-by: Cursor <cursoragent@cursor.com> * Cap geohash nickname cache from remote Nostr events. FIFO-evict at capacity, clear on channel switch, and prune nicknames that leave the visible participant list. Co-authored-by: Cursor <cursoragent@cursor.com> * Avoid overlapping exclusive access in the rate limiter. Make bucket helpers static so inout dictionary updates do not conflict with a mutating call on self. Co-authored-by: Cursor <cursoragent@cursor.com> * Fix rate-limiter tests for mutating allow under #expect. Call allow outside the macro so Swift Testing does not capture an immutable copy of the struct. Co-authored-by: Cursor <cursoragent@cursor.com> * Drop unused WebSocket data helper; reset rate limiter on panic wipe. dataWithinInboundLimit replaced the unbounded path, and panic clear should not leave public intake buckets behind. Co-authored-by: Cursor <cursoragent@cursor.com> --------- Co-authored-by: Cursor <cursoragent@cursor.com>
bitchat
A decentralized peer-to-peer messaging app with dual transport architecture: local Bluetooth mesh networks for offline communication and internet-based Nostr protocol for global reach. No accounts, no phone numbers, no central servers. It's the side-groupchat.
License
This project is released into the public domain. See the LICENSE file for details.
Features
- Dual Transport Architecture: Bluetooth mesh for offline + Nostr protocol for internet-based messaging
- Location-Based Channels: Geographic chat rooms using geohash coordinates over global Nostr relays
- Intelligent Message Routing: Automatically chooses best transport (Bluetooth → Nostr fallback)
- Decentralized Mesh Network: Automatic peer discovery and multi-hop message relay over Bluetooth LE
- Privacy First: No accounts, no phone numbers, no persistent identifiers
- Private Message End-to-End Encryption: Noise Protocol for mesh, NIP-17 for Nostr
- IRC-Style Commands: Familiar
/slap,/msg,/whostyle interface - Universal App: Native support for iOS and macOS
- Emergency Wipe: Triple-tap to instantly clear all data
- Performance Optimizations: LZ4 message compression, adaptive battery modes, and optimized networking
Technical Architecture
BitChat uses a hybrid messaging architecture with two complementary transport layers:
Bluetooth Mesh Network (Offline)
- Local Communication: Direct peer-to-peer within Bluetooth range
- Multi-hop Relay: Messages route through nearby devices (max 7 hops)
- No Internet Required: Works completely offline in disaster scenarios
- Noise Protocol Encryption: End-to-end encryption with forward secrecy
- Binary Protocol: Compact packet format optimized for Bluetooth LE constraints
- Automatic Discovery: Peer discovery and connection management
- Adaptive Power: Battery-optimized duty cycling
Nostr Protocol (Internet)
- Global Reach: Connect with users worldwide via internet relays
- Location Channels: Geographic chat rooms using geohash coordinates
- 290+ Relay Network: Distributed across the globe for reliability
- NIP-17 Encryption: Gift-wrapped private messages for internet privacy
- Ephemeral Keys: Fresh cryptographic identity per geohash area
Channel Types
mesh #bluetooth
- Transport: Bluetooth Low Energy mesh network
- Scope: Local devices within multi-hop range
- Internet: Not required
- Use Case: Offline communication, protests, disasters, remote areas
Location Channels (block #dr5rsj7, neighborhood #dr5rs, country #dr)
- Transport: Nostr protocol over internet
- Scope: Geographic areas defined by geohash precision
block(7 chars): City block levelneighborhood(6 chars): District/neighborhoodcity(5 chars): City levelprovince(4 chars): State/provinceregion(2 chars): Country/large region
- Internet: Required (connects to Nostr relays)
- Use Case: Location-based community chat, local events, regional discussions
Direct Message Routing
Private messages use intelligent transport selection:
-
Bluetooth First (preferred when available)
- Direct connection with established Noise session
- Fastest and most private option
-
Nostr Fallback (when Bluetooth unavailable)
- Uses recipient's Nostr public key
- NIP-17 gift-wrapping for privacy
- Routes through global relay network
-
Smart Queuing (when neither available)
- Messages queued until transport becomes available
- Automatic delivery when connection established
For detailed protocol documentation, see the Technical Whitepaper.
Setup
Option 1: Using Xcode
cd bitchat
open bitchat.xcodeproj
To run on a device there're a few steps to prepare the code:
- Clone the local configs:
cp Configs/Local.xcconfig.example Configs/Local.xcconfig - Add your Developer Team ID into the newly created
Configs/Local.xcconfig- Bundle ID would be set to
chat.bitchat.<team_id>(unless you set to something else)
- Bundle ID would be set to
- Entitlements need to be updated manually (TODO: Automate):
- Search and replace
group.chat.bitchatwithgroup.<your_bundle_id>(e.g.group.chat.bitchat.ABC123)
- Search and replace
Option 2: Using just
brew install just
Want to try this on macos: just run will set it up and run from source.
Run just clean afterwards to restore things to original state for mobile app building and development.
Localization
- Base app resources live under
bitchat/Localization/Base.lproj/. Add new copy toLocalizable.stringsand plural rules toLocalizable.stringsdict. - Share extension strings are separate in
bitchatShareExtension/Localization/Base.lproj/Localizable.strings. - Prefer keys that describe intent (
app_info.features.offline.title) and reuse existing ones where possible. - Run
xcodebuild -project bitchat.xcodeproj -scheme "bitchat (macOS)" -configuration Debug CODE_SIGNING_ALLOWED=NO buildto compile-check any localization updates.